The invention described herein relates generally to semiconductor devices and processing. In particular, the present invention relates to methods, materials, and structures used in forming anti-reflective coatings used in photolithographic processes. More particularly, the invention relates to methods, materials, and structures for forming silicon oxycarbide and silicon carbide anti-reflective coatings on a substrate.
Conventional methods for defining patterns on wafers include photolithographic technologies. Reticle patterns are projected onto photoresist materials layered on the substrate. After the exposure, the photoresist material is developed and unexposed or exposed portions of the photoresist material are removed to form a pattern, defined by the reticle pattern. This pattern can then be transferred onto the substrate surface. In one common implementation, a patterned photoresist layer serves as an etch mask for etching processes used to form patterns on the underlying surface of the substrate.
As greater and greater circuit densities are sought in semiconductor fabrication, greater pattern definition and resolution are needed in photolithographic techniques. As feature size and critical dimension size continue to shrink, the emphasis on achieving greater photolithographic resolution continues. To achieve these goals, photoresist patterns should be sharp enough to permit the formation of extremely accurate patterns in the underlying photoresist layer.
One approach to defining sharp photoresist patterns involves the formation of a bottom anti-reflective coating (BARC) on the substrate surface, but underneath the photoresist layer. A pattern of increased sharpness can then be formed in the photoresist layer by exposing the photoresist material to light of an appropriate wavelength. During photolithography processes, the underlying BARC absorbs light that is projected toward wafers and reduces reflection from the substrate surface thereby increasing pattern resolution in the photoresist. This, in turn, translates into sharper patterns on the substrate surface.
One commonly used BARC material includes a silicon oxynitride material. For a time, such materials were effective anti-reflective coating (ARC) materials. However, with increased usage of certain low-K dielectric materials, one of the drawbacks of silicon oxynitride became apparent. The nitrogen contained in silicon oxynitride BARC layers xe2x80x9cpoisonsxe2x80x9d photoresist layers that contact the BARC. This problem is especially apparent when xe2x80x9caggressivexe2x80x9d photoresist materials are used. Examples of such aggressive photoresist materials include, but are not limited to, Acetal photoresists (produced by Sumitomo of Japan) or Escap photoresists (produced by Tokyo Ohka of Japan). Additionally, such silicon oxynitride BARC""s have a tendency to leave undesirable particle residues on the substrates.
Additionally, with the need for greater resolution is the need for better xe2x80x9cswing curvexe2x80x9d performance. A swing curve is a diagram of surface reflectivity (at a chosen wavelength) versus ARC layer thickness. Since surface reflectivity directly impacts the resolution of the photoresist pattern, the swing curve is a measure of resolution versus ARC thickness. In a perfect ARC, the surface reflectivity (resolution) is mininum and constant regardless of the thickness of the ARC layer. Such a curve is a straight horizontal line. For most materials, this is not the case. One of the disadvantages of silicon oxynitride is that its reflectivity is relatively high and its swing curve is not particularly flat. Thus, it is desirable to replace nitrogen-containing ARC materials with other ARC materials. In particular, such ARC materials should be effective at deep ultraviolet (UV) wavelengths, for example, 193 nm (nanometers) and 248 nm.
For the reasons described hereinabove, as well as other reasons, an improved ARC is needed.
In accordance with the principles of the present invention, a method and structure for an improved ARC are disclosed. One embodiment of the present invention is directed to a silicon oxycarbide anti-reflective coating. Such a coating can be used in conjunction with photolithographic processes using 193 nanometer (nm) wavelength exposure sources. Another embodiment is directed to a silicon oxycarbide anti-reflective coating that is treated with oxygen plasma. Yet another embodiment is directed to a silicon carbide anti-reflective coating. Such a coating can be used in conjunction with photolithographic processes using 248 nanometer (nm) wavelength exposure sources.
A method embodiment for forming an anti-reflective coating on a semiconductor substrate surface comprises depositing the silicon carbide layer on the substrate surface by plasma enhanced chemical vapor deposition. Particularly, the method includes the operations of introducing precursor materials comprising silicon compounds and methyl group containing compounds into a process chamber, where they are ignited as plasma and deposited onto the substrate surface as silicon carbide. Particularly suitable precursor materials include methyl silane materials.
Another method embodiment of forming a silicon oxycarbide anti-reflective coating on a substrate surface is disclosed. The method comprises placing the substrate in a suitable process chamber. Precursor materials including silicon-containing compounds and compounds having methyl groups are introduced with an inert carrier gas into the process chamber. Oxygen is also introduced into the process chamber. These materials are ignited into a plasma, and a silicon oxycarbide material is deposited onto the substrate surface to a desired thickness. As above, particularly suitable precursor materials include methyl silanes, such as tri-methyl silanes and tetra-methyl silanes. By regulating the oxygen flow rate, the optical properties of the silicon oxycarbide layer can be adjusted. In another embodiment, the silicon oxycarbide layer can be treated with oxygen plasma.